As a drive source for driving a wiper member, a wiper motor is used in a rear wiper device for wiping a rear window glass mounted on a vehicle such as an automobile. The wiper motor has an electric motor such as a brushed motor. A speed reduction mechanism and a motion conversion mechanism are contained in a gear case mounted on the electric motor. The speed reduction mechanism comprises a worm rotated by the electric motor and a worm wheel meshing with the worm. The rotation of the electric motor is reduced by the speed reduction mechanism and then transmitted to the worm wheel. A turning motion of the worm wheel is converted into a swinging motion by the motion conversion mechanism and transmitted to an output shaft. The wiper member attached to a distal end of the output shaft is swung back and forth within a predetermined angular range.
As such a wiper motor, for example, as described in JP 2006-151092, there are a narrow-angle type (link type) with a narrow range of swing of the wiper member and a wide-angle type (differential gear) with a wide range of swing of the wiper member. The motion conversion mechanism mounted on the wiper motor of the narrow-angle type has a pivoting lever fixed to a proximal end of the output shaft, and a connecting rod converting the turning motion of the worm wheel into the swinging motion and transmitting the swinging motion to the pivoting lever. The connecting rod is rotatably connected to the worm wheel at a position deviating in a radial direction from an axial center of the worm wheel.
On the other hand, the motion conversion mechanism mounted on the wiper motor of the wide-angle type has a output gear (gear wheel) integrally pivoting and a motion conversion member (sector gear) converting the rotary motion of the worm wheel into the swinging motion and transmitting the swinging motion to the output gear. One end portion of the motion conversion member is rotatably connected to the worm wheel at a position deviating in a radial direction from an axial center of the worm wheel and another end is a sector gear portion (gear tooth) meshing with the output gear. A retaining plate (retaining lever) swingably connecting the output shaft and a gear shaft (swinging center axial) set at an axial center of the sector gear portion is set up and retains meshing of the output gear and the sector gear portion.
By the way, a connecting hole is formed in the worm wheel to fit the connecting shaft into at a position deviated in a radial direction from the axial center of the worm wheel, and the forming position of the connecting hole is set based on the wiping range of the wiper member, the position of the output shaft and so on. There is also a known wiper motor in which at least one pair of connecting holes are formed in the worm wheel so that the stopping position of the wipe member can be set at either inverted position. In this case, in the worm wheel of the narrow-angle type, the pair of connecting holes is formed at positions symmetrical to each other from the axial center of the worm wheel. On the other hand, in the worm wheel of the wide-angle type, a pair of connecting holes is formed at positions deviated circumferentially from positions symmetrical to each other from the axial center of the worm wheel by considering meshing between the output gear and the sector gear portion.
Thus, since the wide-angle type and the narrow-angle type have different wiping range of the wiper member or different positional relations between the pair of connecting holes, the positions of the connecting holes formed in the worm wheel are different therebetween. Conventionally, therefore, the worm wheel in which the connecting holes corresponding to the wide-angle type are formed and the worm wheel in which the connecting holes corresponding to the narrow-angle type are formed are prepared separately so to respond to either the wide-angle type or the narrow-angle type. However, since the increase of the number of types of worm wheels increased, complicated parts control, complicated mold change work because of an increase in the number of molds or inserts, the productivity of wiper motor decreased or cost increased.
An object of the present invention is that a worm wheel can be used in both cases that the output shaft swings in a first swinging range and that the output shaft swings in a second swinging range, thereby improving the productivity of the wiper motor.